Plural component dispensing systems are used in many manufacturing applications. For example, plural component spraying systems have been used in manufacturing plastic articles by applying resinous materials to a mold or a preform for the article. In such systems, a liquid resin and a catalyst for the resin are formed into spray particles directed to a substrate where the catalyst and resin react and harden to form the articles. In such applications, two components, for example, a resin and a catalyst, are mixed together, either internally or externally of a sprayer, and the mixture is applied on the substrate.
Plural component fluid dispensing systems have also been used, for example, in the manufacture of insulating foams. In such systems, first and second liquid components, for example, a polyol resin and an isocyanate, are mixed and after mixing dispensed or sprayed into or onto an article of manufacture where the mixed components react to produce a hardened insulating foam.
More recently, plural component painting systems have been developed that apply plural liquid fluid components that react, when mixed, to form hardened, decorative and protective coatings. Other applications for plural component dispensing systems are continuing to arise with the development of new plural component materials.
Plural component dispensing systems for plural component materials are divided generally into two categories, those in which the multiple components are mixed externally to the system apparatus (referred to as external mix systems) and those in which the plural components are mixed within the system apparatus (referred to as internal mix systems). In both external mix and internal mix systems, it is important that the components be supplied for mixing at the precise ratios recommended by the plural component material manufacturers for curing the mixed plural component material. In addition, fluid dispensing systems should be adjustable to vary widely the ratios between the fluid components of the plural component material; for example, plural component fluid dispensing systems must be capable of mixing and dispensing materials with ratios from 1:1 to as high as about 16:1.
Compressed air is generally available in manufacturing facilities for the operation of various power-driven hand tools that are frequently used in manufacturing operations. It is convenient and desirable that liquid dispensing systems be adapted to operate from such compressed air, which is frequently referred to as "factory air". Thus, liquid delivery systems frequently include a control which is connected with the factory air, and flows of compressed air are directed and controlled by the liquid dispensing system control to operate and control valves and pumps of the liquid dispensing system.
The dispensers of plural component dispensing systems are generally supplied with the plural components by a plural component liquid delivery system which maintains the components separate and apart from each other until they are mixed. The plural component delivery systems frequently include first and second delivery tanks for storing supplies of the components to be mixed. Proportioning pumps are provided to deliver each component to the dispenser of the system at the precise desired flow volume.
In most systems, the proportioning pumps generally comprise positive displacement pumps, frequently reciprocating piston pumps, which are driven from a single air motor by a common interconnecting mechanism in a proportioning pump assembly. The proportioning pump assembly permits each of the positive displacement pumps to be mounted between an assembly base and the common mechanism in a variety of positions that provide variations in the ratio of the components as each of the component pumps is operated by the air motor through the common interconnecting mechanism. By varying the mechanical interconnection of each component pump between the base and the common interconnecting mechanism that drives the pump, each reciprocating piston of each proportioning pump can be driven through a different stroke length with each stroke of the air pump, and deliver different flow rates of each component.
The liquid dispensing system control can include a motor air control valve that is connected between the source of factory air and the air motor of the liquid dispensing system and is operable to control the flow of air to the air motor and thereby the operation of the positive displacement component pumps of the liquid delivery system. The liquid dispensing system control can also include, for example, a leak relay which controls the application of air pressure from the factory air source to the motor air control valve for operation of the motor air control valve and the air motor. Such a leak relay can be connected to the factory air source and through a small flexible hose with a small air valve on the dispenser so that by operation of the air valve by the system operator through actuation of a mechanical actuator such as a trigger, a flow of air can be established from the factory air source through the leak relay, which will operate the motor air control valve and thereby operate the air motor and component pumps. The mechanical actuator of the dispenser can also simultaneously operate a fluid valve or valves controlling the flow of the plural components through the dispenser for application by the system operator. Plural component dispensing systems frequently include an air driven actuator on the dispenser for operation of component flow control valves carried by the dispenser.
In some systems, the liquid delivery systems include heat exchangers and heated hoses to heat and maintain an elevated temperature of the components of a plural component material for delivery of the dispenser. In addition, some liquid delivery systems include components permitting the recirculation of the plural component materials, whether heated or unheated, between the dispenser and their sources.
Examples of systems like those described above are disclosed in U.S. Pat. Nos. 4,760,956; 4,809,909; 4,824,017; 5,080,283; and 5,178,326.
Preferably, plural component dispensing systems are intended to effectively and efficiently deliver, at substantially constant and preselected rates, all components of the plural component materials. Such systems would ensure the delivery of the correct ratio of components at the dispenser in order to dispense materials that provide a properly and completely cured article. However, actual operation of a plural component dispensing system sometimes results in conditions that vary the desired component flow ratio and can result in partially cured or uncured articles. It is important to avoid operation under such conditions and for an operator to be made aware of any unacceptable variation in the flow ratio of components so that the condition can be corrected while minimizing the amount and impact of uncured or partially cured articles. Such unacceptable changes in the flow ratio of the components can occur, for example, because of a blockage in the system or simply running out of one of the components of the plural component material. A plural component dispensing system that interrupts operations under such conditions or that provides an operator with an audible warning of an unacceptable flow or flow ratio or the ability to shutdown the system incoming air would be welcome by users of plural component dispensing systems.